The optical properties of PLZT (lead-lanthinumzirconium-titanate) materials have been widely known for a number of years. Specifically, it has been known that PLZT materials exhibit optical birefringence, a phenomenon which results in the rotation of the plane of polarization of polarized light passing through the material. Furthermore, it has been known that the birefringence of PLZT materials is related to the strength of an electric field imposed perpendicular to the direction of propagation of the light.
These well known properties of PLZT materials have lead to a large number of applications. Electronically controlled optical shutters are a prime example of such applications. However, the use of PLZT materials has been significantly limited by several factors. First, the electric field strength necessary to provide a useful amount of rotation of polarized light is relatively high. Practical devices using PLZT have operated at at least several tens of volts and most often several hundreds of volts. Second, PLZT materials tend to be extremely brittle and unable to withstand significant thermal shocks. These practical problems with PLZT materials have, up to the present, prevented their use as the substrate for large scale, flat panel displays. Such displays require a relatively large array of small, closely spaced display elements or pixels. In order to be able to individually control each pixel, it is necessary to have some type of active device, such as a transistor, at each pixel location. Such integrated displays are widely known using other technologies, such as liquid crystals or electroluminecent phosphors. These displays are feasible because it is possible to fabricate thin film transistors on appropriate substrates which are capable of handling the voltage necessary to drive liquid crystal and electroluminecent displays. However, it has not been possible to fabricate a silicon thin film transistor having sufficiently high voltage characteristics on a PLZT substrate.